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<a name="PACK-_002d_002d_002d-Pack-an-array-into-an-array-of-rank-one"></a>
<h3 class="section">8.212 <code>PACK</code> &mdash; Pack an array into an array of rank one</h3>
<a name="index-PACK"></a>
<a name="index-array_002c-packing"></a>
<a name="index-array_002c-reduce-dimension"></a>
<a name="index-array_002c-gather-elements"></a>

<dl compact="compact">
<dt><em>Description</em>:</dt>
<dd><p>Stores the elements of <var>ARRAY</var> in an array of rank one.
</p>
<p>The beginning of the resulting array is made up of elements whose <var>MASK</var> 
equals <code>TRUE</code>. Afterwards, positions are filled with elements taken from
<var>VECTOR</var>.
</p>
</dd>
<dt><em>Standard</em>:</dt>
<dd><p>Fortran 90 and later
</p>
</dd>
<dt><em>Class</em>:</dt>
<dd><p>Transformational function
</p>
</dd>
<dt><em>Syntax</em>:</dt>
<dd><p><code>RESULT = PACK(ARRAY, MASK[,VECTOR])</code>
</p>
</dd>
<dt><em>Arguments</em>:</dt>
<dd><table>
<tr><td width="15%"><var>ARRAY</var></td><td width="70%">Shall be an array of any type.</td></tr>
<tr><td width="15%"><var>MASK</var></td><td width="70%">Shall be an array of type <code>LOGICAL</code> and 
of the same size as <var>ARRAY</var>. Alternatively, it may be a <code>LOGICAL</code> 
scalar.</td></tr>
<tr><td width="15%"><var>VECTOR</var></td><td width="70%">(Optional) shall be an array of the same type 
as <var>ARRAY</var> and of rank one. If present, the number of elements in 
<var>VECTOR</var> shall be equal to or greater than the number of true elements 
in <var>MASK</var>. If <var>MASK</var> is scalar, the number of elements in 
<var>VECTOR</var> shall be equal to or greater than the number of elements in
<var>ARRAY</var>.</td></tr>
</table>

</dd>
<dt><em>Return value</em>:</dt>
<dd><p>The result is an array of rank one and the same type as that of <var>ARRAY</var>.
If <var>VECTOR</var> is present, the result size is that of <var>VECTOR</var>, the
number of <code>TRUE</code> values in <var>MASK</var> otherwise.
</p>
</dd>
<dt><em>Example</em>:</dt>
<dd><p>Gathering nonzero elements from an array:
</p><div class="smallexample">
<pre class="smallexample">PROGRAM test_pack_1
  INTEGER :: m(6)
  m = (/ 1, 0, 0, 0, 5, 0 /)
  WRITE(*, FMT=&quot;(6(I0, ' '))&quot;) pack(m, m /= 0)  ! &quot;1 5&quot;
END PROGRAM
</pre></div>

<p>Gathering nonzero elements from an array and appending elements from <var>VECTOR</var>:
</p><div class="smallexample">
<pre class="smallexample">PROGRAM test_pack_2
  INTEGER :: m(4)
  m = (/ 1, 0, 0, 2 /)
  ! The following results in &quot;1 2 3 4&quot;
  WRITE(*, FMT=&quot;(4(I0, ' '))&quot;) pack(m, m /= 0, (/ 0, 0, 3, 4 /))
END PROGRAM
</pre></div>

</dd>
<dt><em>See also</em>:</dt>
<dd><p><a href="UNPACK.html#UNPACK">UNPACK</a>
</p></dd>
</dl>



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